Surfriding need alittle help; stupid questions

[ajmps1]

got a ported(unknown) 61x cyl(81.5m bore) with broken off exh studs and two helicoils so, i got 83mm pistons and dropped the cyl off today at powerseal usa. a local cyl repair shop. they are going to bore and hone to 83m bore and drill and tap the exh to 62t thread size. my current setup is a std bore t/t motor with ada girdled head running 35cc domes. i forgot to measure the exhaust ports but my question is what should i do with the domes? what is a good compression to run? send them to zero or buy 760 domes? i think i want the compression to be just under the acceptable limit of pump gas (93 octane) also how will this effect my carb tuning?

preemptively, thank you guys

andy

 

[Matt_E]

The 701 domes are good to 83 - 83.5 mm. You should definitely check the squish once it's bored.
Also, I don't know how familiar that machine shop is with boring 2-strokes. But all the ports need to be chamfered after they bore the cylinder. It's easy to do, so if they do not do it, let them tell you so you can do it yourself. Otherwise you'll snag rings.

If you do order 84mm domes (760), keep in mind that the octane requirements they list on ADA's website for those 760 domes are a bit higher than the 701 domes. You could probably still get away with 35cc domes, but maybe you can get some 36cc domes custom-machined.

 

[Freakrider]

Good info Matt, I am running 701/ 35 cc domes on 83mm bore and it will give you 200 to 205 cranking psi. Running 93 pump gas on enhancer and now on an epic. No problems with that compression for years.

 

[ajmps1]

They said they will chamfer everything. If they dont thats simple enough to do. Thanks matt.E
What carb setup are u running freakrider? What kind of porting? 200psi scares me haha

 

[Freakrider]

44's with XS porting, 200 psi is not a problem on sj / standup hulls because the load is not much compared to a blaster or couch hull. Jetmaniac has run 225 pump gas and besides are you doing wide open runs on it ? Also if your cyl is decked on top compression will be higher, mine is not decked.

 

[Matt_E]

Compression aside, once you get to the bore limit of the dome - which you are with an 83.0mm cylinder bore and 701 domes - you get to the limits of the squish band. Remember, it's angled and a larger cylinder bore gets closer and closer to the tightest squish band at the very outside of the dome.
An overly tight squish may cause detonation way before compression per say would.

 

[ajmps1]

I want a reliable surf boat... I will have the domes cut then. I would rather sacrifice on power then be at the limit of my motor. Will decking it change that much? Its just to make sure there is a level flat surface for the orings to sit on. I cant imagine that much material will need to be removed

 

[JetManiac]

701/35cc domes are fine for 83mm bore. If you want to lower compression just buy 37cc domes and sell your 35's. Much more cost effective than machining domes.

760 domes are for 84mm bore and up. You can bore your cyl later to 84mm and swap to 760 domes no problem. My motor is at 84mm on 61x cylinder for 1 1/2 years of hard use w/o issue.

 

[westjon86]

I've got a similar question. Currently finishing up a build for my blaster. 760 ported and bored to 84.5 by art at jetworks. I want be able to run on 93 without any limitation on WOT runs. I initially was going to use 40cc domes, but he suggested going to 37cc. I have both sets of domes now and can't decide what to do. I know he would know best since he did the work, but just wanted to get some additional feedback.

 

[ajmps1]

What would i want the squish to be chris? I do have some long run outs tho where i ride and will push it alittle. I got wiseco pistons...still also how does this effect the carbs? Oem 38s

 

[JetManiac]

What would i want the squish to be chris? I do have some long run outs tho where i ride and will push it alittle. I got wiseco pistons...still also how does this effect the carbs? Oem 38s

.045-.05 is good. Make sure you arent lean on top for wide open use. Make sure to blip throttle to bring down peak exh temps. You need to jet carbs for your exact setup- pipe, head, f/a type, other mods, etc.

 

[ajmps1]

Ok ill see how it goes when i get her together. Im running oem intake, ada head, oem cdi(for now), factory ltd chamber. And of course 38s aand soon to be 83m 61x from a std bore 62t